Production of tobacco sheets



United States Patent PRODUCTION OF TOBACCO SHEETS Walter G. Frankenburg,Millersville, and Alfred M. Gottscho, Lancaster, Pa., assignors toGeneral Cigar go klnc, New York, N. Y., a corporation of New or a NoDrawing. Application September 23, 1955 Serial No. 536,294

6 Claims. (Cl. 131-140) This application is a continuation-in-part ofour copending application Serial No. 378,722, filed September 8, 1953,now U. S. Patent 2,747,583, issued May 29, 1956.

This invention relates to the continuous manufacture of thin tobaccosheets, particularly sheets made of tobaccos used in cigarettes.

Going back over a period of more than fifty years, there have beennumerous proposals for the conversion of tobacco into sheets in order toutilize portions of the tobacco plant previously discarded as well astobacco waste resulting from the processing of tobacco, but theseproposals have failed to achieve commercial success because the tobaccosheets produced thereby were not acceptable to smokers. Recently,however, commercial production of tobacco sheets has been establishedbased on the teachings of U. S. Patents 2,592,553 and 2,592,554, issuedApril 15, 1952 to W. G. Frankenburg and P. W. Garbo. Our copendingapplication discloses apparatus which was developed for the large-scaleand economic production of tobacco sheets in accordance with theprocesses of U. S. Patents 2,592,553 and 2,592,554. As brought out inour copending application, an aqueous paste or suspension of powderedtobacco and a binding agent is applied as a thin coating on a movingbelt which passes through a drying zone wherein the wet coating iscontacted by a flow of heated and relatively dry air to convert the wetcoating into a dry, coherent film or sheet.

The commercial operation pursuant to our copendiug application for theproduction of tobacco sheets used as binders in the manufacture ofcigars and cigarillos has aroused the interest of the cigarette industryin achieving a low-cost and large-scale production of tobacco sheetssuitable for use in the manufacture of cigaretes.

Extensive experimentation with the aim of achieving the goal of thecigarette industry has revealed that the types of tobacco and tobaccowaste products which would be utilized in the production of tobaccosheets for cigarettes present new problems not encountered with thetobaccos which are used in the manufacture of cigars.

Additionally, the tonnages of tobacco sheets required by the cigaretteindustry far exceed those of the cigar industry; this difference intonnages emphasizes the need to use a binding agent which is availablein abundant supply and at a low price. The foregoing factors requiringattention for the commercial production of cigarette tobacco sheets arelargely independent of still another factor which stems from the lowervalue of cigarettes as compared with cigars. The latter point involvesthe need to accelerate the rate of production as much as possible sothat large tonnages of cigarette tobacco sheets may be obtained, whileavoiding an unreasonably large 'manufacturing plant and high capitalcost.

Experimentationhas shown that tobaccos, such as flue- -cured and Turkishtobaccos, which are used in the manufacture of cigarettes, substantiallyincrease the difiicul- -ties of making goodrtobacco sheets.Specifically, ciga- 'ice rette tobaccos tend to yield weaker sheets ofgreater adhesion to the surface on which they are formed. Because oflower strength and higher adhesion, it is often impossible to removefrom the supporting surface the dry tobacco coating as a continuoustobacco sheet. Furthermore, as brought out in our copending application,a very satisfactory tobacco sheet is made by using methyl cellulose of4000 centipoise type or grade. This is a premium grade of methylcellulose, and consequently, more expensive than standard grade methylcellulose, i. e., 400 centipoise type.

Accordingly, a principal object of this invention is to provide acontinuous, rapid process for producing large tonnages of cigarettetobacco sheets at an economically attractive cost.

In accordance with this invention, a tobacco sheet suitable for themanufacture of cigarettes is made by dissolving about 2.2% to 2.6% byweight of 400 centipoise grade methyl cellulose in water, admixing theresulting solution with dry-ground tobacco in the proportions of 2.5 to4.5 parts by weight of the aqueous solution to each part of tobacco,applying the resulting viscous mixture as a thin coating on a metalsurface, drying the coating by contact with air heated to a temperaturein the range of F. to 160 F., and removing from the metal surface thethus dried coating as the desired tobacco sheet. In accordance with ourcopending application, the drying operation is preferably conducted intwo stages; in the first stage, the wet coating is contacted with air ata temperature in the range of F. to F. and having a relative humiditynot exceeding about 25%, while in the second stage, the air is at atemperature about 10 F. to 15 F. lower than that of the first stage butnot lower than 110 F. and has a relative humidity in the range of 12% to25%.

By employing 400 centipoise type methyl cellulose, not only is the costof the binding agent reduced as compared with the 4000 centipoise type,but also it has become possible to curtail substantially the amount ofwater used in preparing the tobacco suspension or paste in order toshorten the drying time. At the restricted aqueous solution-to-tobaccoratios employed in the process of this invention, the higher grades ofmethyl cellulose yield such viscous and stiff tobacco pastes that r theycannot be applied properly as a thin coating to the surface of a metalbelt which conveys the coating to the drying zones. Both for economicand smoking considerations, the cigarette industry requires tobaccosheets with a minimum content of binding'agent; by limiting the contentof 400 centipoise grade methyl cellulose in water to the range of about2.2% to 2.6% by weight, the requirement of the cigarette industry iseasily satisfied because at aqueous solution-to-tobacco weight ratios of2.5 :1 to 4.521 it becomes possible to produce tobacco sheets containingnotmore than 10% preferably not more than 8%, of methyl cellulose, basedon the Weight of the dry-ground tobacco used in making the sheets. Inshort, the desired proportion of methyl cellulose to tobacco in thefinished tobacco sheet is readily obtained by selecting a concentrationof methyl cellulose in water and an aqueous solution-to-tobacco weightratio, within the 3 when spread on a metal surface and dried, adherestrongly to the surface, making it very difiicult to remove the driedcoating as a continuous sheet. Furthermore, cigarette tobaccos tend togive weaker tobacco sheets than do cigar tobaccos used in similarformulations. Often, the cigarette tobacco will yield a tobacco sheet ofvery dark and disagreeable color, as well as one having a'high crackingpropensiy. Correction of the tendency of cigarette tobaccos to formsheets which crack readily and are of disagreeable appearance may beachieved by following the teachings of copending application Serial No.510,851, filed May 24, 1955, by W. G. Frankenburg and P. H. Waltz. Theapplication of Frankenburg and Waltz discloses that the addition of aminor amount of acid to a paste of powdered tobacco and an aqueoussolution of a cellulose derivative like methyl cellulose will preventthe occurrence of the difiiculties previously encountered in theutilization of cigarette tobaccos. While an inorganic acid likephosphoric or boric acid may be used, organic acids, particularlyhydroxylated polybasic carboxylic acids, such as citric, malic andtartaric acids, are generally preferred. The amount of acid used in thetobacco paste is generally not more than 5% by weight, based on thetobacco present therein. Frequently, 2% to 3% of acid yields verysatisfactory results. The acidified tobacco paste usually has a pH inthe range of 3.0 to 5.5.

Methyl cellulose is graded, according to the viscosity, measured incentipoises at a temperature at 25 C., of an aqueous solution containing2% by weight of the methyl cellulose. Material marketed as 400centipoise type methyl cellulose commonly embraces methyl eelluloseswhich in 2% by weight aqueous solutions give viscosities at 25 C. in therange of 300 centipoises to 500 centipoises. Consequently, the aqueoussolutions containing from 2.2% to 2.6% by weight of methyl cellulose asprepared in accordance with this invention have viscosities in the rangeof about 400 centipoises to 1200 centipoises.

It is well to note that while the aqueous solution of methyl cellulosehas a viscosity of 400 centipoises to 1200 centipoises at 25 C., thesame solution after admixture with the powdered tobacco in the specifiedproportions will have ,a substantially higher viscosity, i. e., over6000 centipoises. In order that the tobacco paste may be properlyapplied as a thin film or coating on a supporting surface, it shouldhave a viscosity not exceeding about 35,000 centipoises; tobacco pasteviscosi ties in the range of 12,000 centipoises to 28,000 centipoisesare generally preferred. At these viscosities, the

formed generally increases with the total content of carbohydrates,pectins and pentosans of the tobacco used in making the sheets. Whilethe content of these substances in any type of tobaceowill vary with theplant strain, growing conditions, leaf position and similar factors,average values of the total content of carbohydrates, pectins andpentosans for the several types of tobacco fall in thefollowing ranges:

Type of tobacco: Total content Flue-cured 25% to 38% by weight. Turkish20% to 30% by weight. Burley 16% to 20% by weight. Maryland to 22% byweight.

Cigarette tobacco sheets are distinctly more difiicult to produce whenmade of flue-cured or Turkish tobaccos (i. e., tobaccos with a totalcontent of carbohydrates,

.pectins and-pentosans of at least%' by weight) than when made of burleyor Maryland tobaccos. Cigar tobaccos generally have total contents ofcarbohydrates, pectins and pentosans below 15% by weight and rarely givethe sheet-forming difficulties, like strong adhesion to the supportingsurface, high cracking propensity and disagreeable appearance, which areencountered with cigarette tobaccos. While the cracking and colordifficulties with cigarette tobacco sheets are substantially overcome byacidifying the tobacco paste before it is spread out as a thin film anddried, the problem of removing the adherent dry film from the supportingsurface as a continuous tobacco sheet remains as a serious obstacle tolarge-scale commercial operation. The latter problem now also vanisheswhen powdered cigarette tobacco is admixed with an aqueous solutioncontaining 2.2% to 2.6% by weight of 400 centipoise grade methylcellulose. Cigarette tobacco sheets made with 400 centipoise grademethyl cellulose in accordance with this invention show good tensilestrength and are readily stripped from the supporting surfaces on whichthey are formed, particularly after the dry sheets have been moistenedby a fine water mist.

The tobacco sheets produced in accordance with this invention desirablycontain the non-water-swelling siliceous catalysts disclosed in U. S.Patent 2,706,695, granted April 19, 1955 to W. G. Frankenburg. Likewise,it is advisable to include plasticizers like glycerine and the glycolsin the formulation of the tobacco sheets in order to increase theirflexibility.

By restricting the quantity of aqueous solution of methyl cellulose thatis admixed with the powdered tobacco to the range of 2.5 to 4.5 parts byweight for each part of tobacco, the drying time is substantiallycurtailed. Heretofore, tobacco sheets were produced with a drying timeof about 4 minutes, whereas this invention makes it feasible to operatewith a drying time of not more than 2 minutes.

For a better understanding of the invention, illustrative embodimentsare presented hereinbelow in detail.

Example 1 An aqueous solution containing 2.2% by weight of 400centipoise grade methyl cellulose is admixed with powdered tobaccoconsisting on a weight basis of of tobacco dust recovered from theprocessing of Turkish cigarette tobacco and 20% of dry-ground burleytobacco stems. The methyl cellulose solution is admixed with thepowdered tobacco in the weight proportions of 4.1 parts of solution toeach part of powdered tobacco; in other words, the methyl celluloseamounts to about 9% by weight based on the tobacco. To the resultingtobacco paste, the following ingredients are added in the proportionsindicated:

Citric acid 5% by Weight based on the tobacco.

Diatomaceous earth 7% by weight based on the tobacco.

Triethylene glycol 11% by weight based on the tobacco.

Siliceous catalyst 75% by weight based on the methyl cellulose.

The paste containing all of the ingredients has a viscosity of about28,000 centipoises at 25 C. and is applied by a reverse roll coater as athin coating to a stainless steel belt which conveys the coating(approximately 0.01 inch thick) through two drying zones arranged inseries. The coating of tobacco paste on the belt is contacted in thefirst zone for 0.8 minute with air heated to a temperature of 150 F. andhaving a relative humidity of approximately 15%. The partially driedcoating then passes through the second zone wherein it is contacted foranother 0.8 minute with air heated to a temperature of F. and having arelative humidity of about 20%. Onleaving the second drying zone,thevisuallydry coating on the conveyor belt is moistened by a fine Watermist so that the coating then has a moisture content of approximately30% by weight. In this condition, the coating is easily peeled off thesupporting belt and is ready for use in the manufacture of cigarettes.The cigarette tobacco sheet thus produced has good tensile strength, isapproximately 0.003 inch in thickness and has an attractive tobacco-likeappearance.

Example 2 An aqueous solution containing 2.58% by weight of 400centipoise grade methyl cellulose is admixed with powdered tobaccoconsisting on a weight basis of 70% of tobacco dust recovered from theprocessing of mixed cigarette tobaccos predominantly of the flue-curedtype and 30% of dry-ground winnower slivers (i. e., small pieces ofstems), derived from the cigarette tobaccos. The methyl cellulosesolution is admixed with the powdered tobacco in the weight proportionsof 2.85 parts of solution to each part of powdered tobacco; in otherwords, the methyl cellulose amounts to about 7.35% by Weight based onthe tobacco. To the resulting tobacco paste, the following ingredientsare added in the proportions indicated:

Citric acid 5% by weight based on the tobacco. Diethylene glycol 13% byweight based on the tobacco. Siliceous catalyst 100% by weight based onthe methyl cellulose.

The paste containing all of the ingredients has a viscosity of about22,000 centipoises at 25 C. and is applied by a reverse roll coater as athin coating to a stainless steel belt which conveys the coating(approximately 0.01 inch thick) through two drying zones arranged inseries. The coating of tobacco paste on the belt is contacted in thefirst zone for 0.7 minute with air heated to a temperature of 145 F. andhaving a relative humidity of approximately 18%. The partially driedcoating then passes through the second zone wherein it is contacted foranother 0.7 minute with air heated to a temperature of 133 F. and havinga relative humidity of about 16%. On leaving the second drying zone, thevisually dry coating on the conveyor belt is moistened by a fine watermist so that the coating then has a moisture content of approximately32% by weight. In this condition, the coating is easily peeled off thesupporting belt and is ready for use in the manufacture of cigarettes.The cigarette tobacco sheet thus produced has good tensile strength, isapproximately 0.003 inch in thickness and has an attractive tobacco-likeappearance.

Those skilled in the art will visualize several modifications andvariations of the invention set forth hereinabove without departing fromits spirit and scope. Accordingly, the claims should not be interpretedin any restrictive sense other than that imposed by the limitationsrecited within the claims.

What is claimed is:

1. A process for producing a tobacco sheet from cigarette tobacco havinga content of carbohydrates, pectins and pentosans totaling at least 15%by weight, which comprises dissolving about 2.2% to 2.6% by weight of400 centipoise grade methyl cellulose in water, admixing the resultingsolution with said cigarette tobacco in powdered form in the proportionsof 2.5 to 4.5 parts by weight of said solution to each part of saidcigarette tobacco to yield a viscous mixture containing not more thanparts by weight of said methyl cellulose for each parts of saidcigarette tobacco, applying said viscous mixture as a thin coating on amet-a1 surface, drying said coating by contact with air heated to atemper ature in the range of to 160 F., moistening the dried coatingwith atomized water, and peeling the moistened coating from said metalsurface as a tobacco sheet.

2. The process of claim 1 wherein the viscous mixture applied as a thincoating has a viscosity in the range of about 12,000 centipoises to28,000 centipoises at a temperature of 25 C.

3. A process for producing a cigarette tobacco sheet which comprisesdissolving about 2.2% to 2.6% by weight of methyl cellulose in water toproduce a solution having a viscosity in the range of 400 centipoises to1200 centipoises at a temperature of 25 C., admixing said solution withdry-ground cigarette tobacco having a con tent of carbohydrates, pectinsand pentosans totaling at least 15% by weight in the proportions of 2.5to 4.5 parts by weight of said solution to each part of said cigarettetobacco to yield a viscous mixture containing not more than 8 parts byweight of said methyl cellulose for each 100 parts of said cigarettetobacco, applying said viscous mixture as a thin coating on a metalsurface, drying said coating by contact with air heated to a temperaturein the range of F. to F., moistening the dried coating wtih atomizedwater, and peeling the moistened coating from said metal surface as acigarette tobacco sheet.

4. The process of claim 3 wherein the cigarette tobacco is flue-curedtobacco and the viscous mixture applied as a thin coating has aviscosity in the range of about 12,000 centipoises to 28,000 centipoisesat a temperature of 25 C.

5. The process of claim 3 wherein the cigarette tobacco has a content ofcarbohydrates, pectins and pentosans totaling at least 20% by weight andthe viscous mixture is acidified to a pH in the range of 3.0 to 5.5before being applied as a thin coating.

6. In a process for producing a tobacco sheet by admixing powderedtobacco with an aqueous solution of methyl cellulose and by drying theresulting aqueous tobacco suspension in the form of a film deposited ona supporting surface, the improvement of accelerating the drying of saidfilm to yield a tobacco sheet that is readily stripped from saidsupporting surface, which comprises dissolving about 2.2% to 2.6% byweight of methyl cellulose in water to produce a solution having aviscosity in the range of 400 centipoises to 1200 centipoises at atemperature of 25 C., admixing not more than 4.5 parts by weight of saidsolution with each part of powdered tobacco to yield a viscous mixturehaving a viscosity in the range of 6000 centipoises to 35,000centipoises at a temperature of 25 C., applying said viscous mixture asa film approximately 0.01 inch thick on a supporting surface, and dryingsaid film in not more than 2 minutes by contact with air heated to atemperature of not more than F.

References Cited in the file of this patent UNITED STATES PATENTS2,433,877 Wells et al Jan. 6, 1948 2,534,113 Egger Dec. 12, 19502,592,553 Frankenburg et a1 Apr. 15, 1952 2,613,673 Sartoretto et al.Oct. 14, 1952 FOREIGN PATENTS 1,026,418 France Feb. 4, 1953

1. A PROCESS FOR PRODUCING A TOBACCO SHEET FROM CIGARETTE TOBACCO HAVINGA CONTENT OF CARBOHYDRATES, PECTINS AND PENTASONS TOTALING AT LEAST 15%BY WEIGHT, WHICH COMPRISES DISSOLVING ABOUT 2.2% TO 2.6% BY WEIGHT OF400 CENTIPOISE GRADE METHYL CELLULOSE IN WATER, ADMIXING THE RESULTINGSOLUTION WITH SAID CIGARETTE TOBACCO IN POWDERED FORM IN THE PROPORTIONSOF 2.5 TO 4.5 PARTS BY WEIGHT OF SAID SOLUTION TO EACH PART OF SAIDCIGARETTE TABACCO TO YIELD A VISCOUS MIXTURE CONTAINING NOT MORE THAN 10PARTS BY WEIGHT OF SAID METHYL CELLULOSE FOR EACH 100 PARTS OF SAIDCIGARETTE TOBACCO, APPLYING SAID VISCOUS MIXTURE AS A THIN COATING ON AMETAL SURFACE, DRYING SAID COATING BY CONTACT WITH AIR HEATED TO ATEMPERATURE IN THE RANGE OF 110*F. TO 160*F., MOISTENING THE DRIEDCOATING WITH ATOMIZED WATER, AND PEELING THE MOISTENED COATING FROM SAIDMETAL SURFACE AS A TOBACCO SHEET.